This project concerns the genetic and epigenetic control of senescence and death at the cellular level in Drosophila melanogaster. We propose to analyze the control and function of localized cell death which occurs during the development of imaginal discs, by analyzing mutations which cause excessive cell death in particular areas. We also plan to use these mutations to induce cell death so that we can further analyze the resulting pattern deletions, duplications, triplications, and fusions. We shall mimic the effects of cell-death mutations by producing patches of cell death with a UV-laser microbeam, to define exactly the distribution of cell death necessary to give the observed phenotypes. We aso propose to study the aging-like changes which occur in imaginal disc tissue cultured in vivo for long periods. These changes include loss or ability to differentiate normal structures, loss of growth control, inability to metamorphose, acquisition of neoplastic properties, and degeneration. We intend to ascertain whether any of these changes in old disc cells can be reserved by direct cell contact and intercellular interaction with young cells.